A “malicious” letter sent to senior officers at Lewisham Council by a “whistle-blower” is being investigated by police.

This letter came after the council began an investigation into allegations of  “improper activity” against a councillor and council officers, to do with the council’s chief executive.

Whistle-blowing is the the council’s most serious complaint channel, through which complaints can be made about council staff, councillors and council contractors.

When asked to give more details, the complainant refused and then sent a “very threatening and extremely intimidating” letter to senior council staff, Lewisham Council head of law Kath Nicholson explained at a standards committee meeting.

“I have referred it to the police, who are investigating. They are satisfied it is malicious communications,” she said.

This comes after Lewisham Council staff were targets of violence from demonstrators protesting outside the New Cross Assembly at the Mulberry Centre in Amersham Vale earlier this month.

A senior council officer’s car was damaged by demonstrators while Lewisham Mayor Damien Egan was inside.

Emotions have been high in Lewisham after the eviction of protestors at the Old Tidemill Wildlife Garden and the council’s announcement that chief executive Ian Thomas would be leaving the role at the end of the year.

A petition calling for more information about why Mr Thomas is leaving the role has reached more than 1,800 signatures.

Mr Thomas started at the council in March.

Speaking at his appointment, then-Mayor of Lewisham Sir Steve Bullock said Mr Thomas was a “highly-regarded local government leader”.

Mr Thomas will remain as  chief executive until December 31 on a £185,000 salary, a council report suggests.

Lewisham Council executive director for resources and regeneration Janet Senior is currently acting chief executive.

Investigation into the complaint and the letter is ongoing.